Conventional rendering devices such as copiers, scanners, and laser printers, (both color and black & white) are widely used as output devices in home and office computers. Such rendering devices are particularly popular in computing environments where relatively high speed is desired. In addition to the demand for high speed, there is also a growing demand for higher quality rendering and printing. However, since these characteristics are generally inversely related, higher quality comes at the expense of slower throughput. That is, the more intensive processing required to produce a higher quality output slows the rendering output rate.
In conventional laser printer systems, for example, an image processing unit can accept input from a printer driver and generates pulse wave modulated (PWM) video data to drive the laser engine. In such systems, the graphics objects are typically first rendered into 24 bits/pixel RGB data and 8 bits/pixel in an X field, where R, G and B respectively represent red, green and blue color intensities and X indicates whether the pixel is a text, graphics or image pixel. Raster operation processing (ROP) instructions are then performed in 24-bit RGB color space. The ROP codes define how the graphics device interface (GDI) combines the bits from the selected pen with the bits in the destination map.
The RGBX data can then be converted into CMYKX data and written to memory in compressed format. At higher output resolutions (e.g., 600 dpi and up) this processing is quite time consuming on conventional systems and tends to create a bottleneck in the processing pipeline. The post-decompression operations provided by color resolution improvement technology (CRIT) and color photo graphic improvement (CPGI), which are used to generate PWM-formatted signals also slow considerably at higher output resolutions.
In order to achiever higher rendering speeds and output, it is sometimes necessary when configuring and designing rendering devices to implement sub-system architecture for image enhancement algorithms for sub-pixel generation. In order to enhance the quality of images rendered by high-speed rendering devices, such as color laser printers or copiers, it is necessary to control the size of the pixels. This can be accomplished by altering the timing and the duration of the laser beam for each particular pixel. Traditionally, the hardware which implements such algorithms utilizes pulse width position modulation. For high speed printers, however current electronics technology limits the speed. Therefore, it is believed that a particular method for implementing the procedure in order to control the degree of further adjustments to optimize the performance under different printing parameters, such as pixel clock frequencies, number of pixels, printing speed and so forth is needed.